1. Field of the Invention
The present invention relates to a developing apparatus used in an image-forming apparatus such as a copier or printer for forming an electrophotographic image, for supplying non-magnetic single component toner to a photoreceptor surface via a developing roller that has a toner layer formed on a circumferential surface thereof by means of pressing force of a blade against the developing roller.
2. Description of the Related Art
In an image-forming apparatus in which an electrostatic latent image formed on a photoreceptor surface by photoconductive action is rendered visible as a toner image, and then the toner image is transferred to a record medium, is used a developing apparatus for supplying toner to the electrostatic latent image formed on the photoreceptor surface. The developing apparatus has a developing roller rotatably disposed, which usually has part of a circumferential surface opposed to the photoreceptor surface. Toner accommodated in the developing apparatus is applied to the circumferential surface of the developing roller, which toner is then conveyed to the photoreceptor surface therefrom. In particular, a developing apparatus of a type designed to supply non-magnetic single component toner to the photoreceptor surface includes a planar plate-like blade that abuts against the circumferential surface of the developing roller to regulate the thickness of a toner layer to be formed on the circumferential surface of the developing roller, by an abutting force of the blade.
In such a developing apparatus used for image formation, using the non-magnetic single component toner, the condition of supply of the toner to the photoreceptor surface is varied, depending upon how the toner layer is formed on the circumferential surface of the developing roller. The condition of formation of the toner layer is varied, depending upon the condition of abutment of the blade against the circumferential surface of the developing roller. Accordingly, the condition of abutment of the blade against the circumferential surface of the developing roller exerts an influence upon the condition of image-formation.
A prior art developing apparatus related to blades is disclosed in, for example, Japanese Unexamined Patent Publication JP-A 5-323778 (1993), which developing apparatus has a blade having a distal end bent at an angle of 0 to 90xc2x0 in a direction in which the blade is spaced apart from the circumferential surface of a developing roller so that the bend of the blade abuts against the circumferential surface of the developing roller to regulate the thickness of the toner layer thereon.
Another type of blade disclosed in Japanese Unexamined Patent Publication JP-A 7-64391 (1995) is bent at a portion or adjacent thereto where a distal end of the blade contacts the circumferential surface of the developing roller. The blade is bent at an obtuse angle (within a range between 0 and 90xc2x0 in a direction in which the blade is spaced apart from the circumferential surface of the developing roller), thereby permitting a toner layer having a uniform thickness to be formed on the circumferential surface of the developing roller.
In a further type of blade disclosed in Japanese Unexamined Patent Publication JP-A 7-239611 (1995), slanted portions of a blade edge at both ends in the width direction of the blade is made smaller in length than another slanted portion of the blade edge at a central portion in the width direction of the blade, thereby increasing a force that permits the blade to regulate the thickness of a toner layer at the both ends of the blade in order to prevent excess toner from passing through between the circumferential surface of the developing roller and the blade. This structure allows the toner layer having a uniform thickness to be formed on the circumferential surface of the roller along the entire length of the blade.
In a yet further type of blade disclosed in Japanese Unexamined Patent Publication JP-A 9-138566 (1997), one curvature radius of the blade at both ends thereof where the blade is positioned against the developing roller is greater than another curvature radius of the blade at a central portion thereof, thereby preventing the occurrence of a toner layer having an irregular thickness, which otherwise would occur as a result of interference of sealing pressure. The sealing pressure is applied to the blade by means of sealing members that are disposed at both ends of the blade.
The developing apparatus using the non-magnetic single component toner must include a blade that serves a dual purpose, i.e., the function of allowing the toner supplied to the circumferential surface of the developing roller to be uniformly charged with a predetermined electric charge as well as the function of permitting the toner layer having a uniform thickness to be formed on the circumferential surface of the developing roller. However, prior art developing apparatus is impossible to serve the former function, although fulfilling the latter function. Consequently, a problem with such conventional developing apparatus is that good image formation is impossible to be always retained.
In view of the above, an object of the invention is to provide a developing apparatus capable of forming a uniformly charged toner layer having a uniform thickness all over an image formation area of a circumferential surface of a developing roller, to maintain good image forming conditions for uniform image density.
In order to achieve the object, the invention is structured as follows.
The invention provides a developing apparatus comprising:
a developing roller for supplying non-magnetic single component toner deposited in a layered fashion on a circumferential surface of the developing roller to a surface of a photoreceptor by rotation of the developing roller at a predetermined speed; and
a planar plate-like blade cantilevered at one end thereof, for regulating thickness of a toner layer by pressing a part of the other end of the blade against the circumferential surface of the developing roller,
the other end of the blade being bent at a bending angle in a direction in which the other end of the blade is spaced apart from the circumferential surface of the developing roller, the bending angle being 45xc2x0 or more,
a bend of the other end of the blade being positioned downstream by an amount of 0.4 mm from a tangent point between the blade and the developing roller with respect to a direction of rotation of the circumferential surface of the developing roller.
In this structure of the developing apparatus according to the invention, the bending angle of the blade, which influences the thickness of the toner layer on the circumferential surface of the developing roller, and the position of the bend of the blade, which influences the specific electric charge of the toner as well as the thickness of the toner layer, are set within a range in which a toner layer having a proper thickness and toner having a proper specific charge are provided. As a result, the toner layer having such a proper thickness is formed on the circumferential surface of the roller, while the toner exhibits such a proper specific charge. Consequently, properly charged toner is supplied in a proper amount to the photoreceptor surface.
According to the invention, the bending angle of the blade, which influences the thickness of the toner layer on the circumferential surface of the developing roller, and the position of the bend of the blade, which influences the specific electric charge of the toner as well as the thickness of the toner layer, are set within a range in which a toner layer having a proper thickness and toner having a proper specific charge are provided. As a result, the toner layer having an optimum thickness is formed on the circumferential surface of the roller, while the toner exhibits an optimum specific charge. Consequently, since desirably charged toner can be supplied in a proper amount to the photoreceptor surface, good image forming conditions can be maintained.
In the invention it is preferable that the bending angle of the other end of the blade is within a range of 75xc2x0 to 90xc2x0.
In this structure of the developing apparatus according to the invention, the bending angle of the other end of the blade, which influences the thickness of the toner layer, is set within a range in which the thickness of the toner layer is made more proper. As a result, the toner layer having such a more proper thickness is provided on the circumferential surface of the roller, and a more proper amount of toner is thereby supplied to the photoreceptor surface.
According to the invention, the bending angle of the other end of the blade, which influences the thickness of the toner layer, is set within a range in which the thickness of the toner layer is made more proper. As a result, the toner layer having a more proper thickness can be provided on the circumferential surface of the developing roller, and a more proper amount of toner can be supplied to the photoreceptor surface.
In the invention it is preferable that the bend of the other end of the blade is positioned downstream by an amount of 0.0 to 1.0 mm from a tangent point between the blade and the developing roller with respect to a direction of rotation of the circumferential surface of the developing roller.
In this structure of the developing apparatus according to the invention, the position of the bend of the blade, which influences the thickness of the toner layer on the circumferential surface of the developing roller as well as the specific electric charge of the toner, is set within a range in which a toner layer having a more proper thickness and toner having a more proper specific charge are provided. As a result, the toner layer having such a more proper thickness is formed on the circumferential surface of the roller, while the toner provides such a more proper specific charge. Consequently, more properly charged toner is supplied in a more proper amount to the photoreceptor surface.
According to the invention, the position of the bend of the blade, which influences the thickness of the toner layer on the circumferential surface of the developing roller as well as the specific electric charge of the toner, is set within a range in which a toner layer having a more proper thickness and toner having a more proper specific charge are provided. As a result, the toner layer having such a more proper thickness is formed on the circumferential surface of the roller, while the toner provides such a more proper specific charge. Consequently, more optimum charged toner can be supplied in a more proper amount to the photoreceptor surface.
In the invention it is preferable that the developing apparatus further comprises sealing members disposed at both ends of the blade in an axial direction of the developing roller, and the other end of the blade is bent in a direction in which the other end of the blade is spaced apart from the circumferential surface of the developing roller such that bending angles of the other end of the blade at both axial ends of the developing roller are different from that at an axial intermediate portion of the developing roller.
In this structure of the developing apparatus according to the invention, bending angles of the ends of the blade which abut against both axial ends of the developing roller are different from the bending angle of the intermediate portion of the blade which abuts against an axial intermediate portion of the developing roller. Accordingly, the bending angles of the blade in the axial direction of the developing roller are set according to an influence of the sealing members on the thickness of the toner layer at the axial ends of the developing roller. As a result, a toner layer having a uniform thickness is formed over the entire area of the developing roller in the axial direction thereof.
According to the invention, bending angles of the ends of the blade which abut against both axial ends of the developing roller provided with the sealing members are different from the bending angle of the intermediated portion of the blade which abuts against an axial intermediate portion of the developing roller. Accordingly, the bending angles of the blade in the axial direction of the developing roller are set according to an influence of the sealing members on the thickness of the toner layer at the axial ends of the developing roller. As a result, a toner layer having a uniform thickness can be formed over the entire area of the developing roller in the axial direction thereof.
In the invention it is preferable that the other end of the blade is bent in a direction in which the other end of the blade is spaced apart from the circumferential surface of the developing roller such that the bending angle of the other end of the blade is varied to be gradually smaller from the axial intermediate portion toward both the axial ends of the developing roller than a predetermined bending angle of the other end of the blade at the axial intermediate portion of the developing roller.
In this structure of the developing apparatus according to the invention, the other end of the blade is bent such that the bending angle is made gradually smaller toward both the axial ends of the developing roller than a predetermined bending angle of the other end of the blade at the axial intermediate portion of the developing roller. Accordingly, an abutting force of the blade against the circumferential surface of the developing roller gradually reduced from the axial intermediate portion of the developing roller to both the axial ends of the developing roller. Then, the abutting force of the blade against the circumferential surface of the roller is equalized over a wide range of the developing roller in the axial direction thereof while abutting forces of the sealing members are exercised on both axial ends of the developing roller.
According to the invention, a bending angle of the other end of the blade is made gradually smaller toward both the axial ends of the developing roller than a predetermined bending angle of the other end of the blade at the axial intermediate portion of the developing roller. Accordingly, an abutting force of the blade against the circumferential surface of the developing roller is gradually reduced from the axial intermediate portion of the developing roller to both the axial ends of the developing roller. As a result, the abutting force of the blade against the circumferential surface of the roller can be equalized over a wide range of the developing roller in the axial direction thereof while abutting forces of the sealing members are exerted on both the axial ends of the developing roller.
In the invention it is preferable that the bending angle of the other end of the blade at both the axial ends of the developing roller is 45xc2x0 or more.
In this structure of the developing apparatus according to the invention, the other end of the blade is bent such that a bending angle of the other end of the blade at both the axial ends of the developing roller gradually is gradually reduced from the predetermined bending angle of the other end of the blade at the axial intermediate portion of the developing roller to the maximum bending angle of 45xc2x0. Accordingly, an abutting force of the blade against the developing roller is gradually reduced with a decrease in bending angle of the other end of the blade at both the axial ends of the developing roller. As a result, a toner layer having a uniform thickness is formed on the circumferential surface of the developing roller over a wide range of the developing roller in the axial direction thereof while abutting forces of the sealing members are exerted on both the axial ends of the developing rollers.
According to the invention, the other end of the blade is such bent that a bending angle of the other end of the blade at both the axial ends of the developing roller gradually is gradually reduced from the predetermined bending angle of the other end of the blade at the axial intermediate portion of the developing roller to the maximum bending angle of 45xc2x0. Accordingly, an abutting force of the blade against the developing roller is gradually reduced with a decrease in bending angle of the other end of the blade at both the axial ends of the developing roller. As a result, a toner layer having a uniform thickness can be formed on the circumferential surface of the developing roller over a wide range of the developing roller in the axial direction thereof while abutting forces of the sealing members are exerted on both the axial ends of the developing rollers.
In the invention it is preferable that the bending angles of the other end of the blade at both the axial ends of the developing roller are greater than that at the axial intermediate portion of the developing roller.
In this structure of the developing apparatus according to the invention, the bending angle of the other end of the blade at both the axial ends of the developing roller is greater than the bending angle of the other end of the blade at the axial intermediate portion of the developing roller. Consequently, the abutting force of the blade against the circumferential surface of the developing roller at both the axial ends of the developing roller is greater than the abutting force of the blade against the circumferential surface of the roller at the axial intermediate portion of the developing roller. As a result, a toner layer having a smaller thickness is formed on the circumferential surface of the developing roller at both axial ends of the developing roller, while a toner layer having a greater thickness is formed thereon at the axial intermediate portion of the developing roller.
According to the invention, the bending angle of the other end of the blade at both the axial ends of the developing roller is greater than the bending angle of the other end of the blade at the axial intermediate portion of the developing roller. Consequently, the abutting force of the blade against the circumferential surface of the developing roller at both the axial ends of the developing roller is greater than another abutting force of the blade against the axial intermediate portion of the developing roller. As a result, a toner layer having a smaller thickness can be formed on the circumferential surface of the developing roller at both axial ends of the developing roller, while a toner layer having a greater thickness is formed thereon at the axial intermediate portion of the developing roller. Consequently, the toner can operatively be blocked from leaving that particular position.
In the invention it is preferable that the bending angles of the other end of the blade at both the axial ends of the developing roller is nearly 90xc2x0.
In this structure of the developing apparatus according to the invention, the other end of the blade is bent at an angle of some 90xc2x0 at both the axial ends of the developing roller. Accordingly, a force of the sealing members to support the bend of the blade in cooperation with the developing roller does not act in a direction in which the blade is forced into contact with and away from the circumferential surface of the roller. As a result, an abutting force of the blade against the circumferential surface of the developing roller is invariable regardless of the presence of the sealing members.
According to the invention, the other end of the blade is bent at an angle of approximately 90xc2x0 at both the axial ends of the developing roller. Accordingly, it is possible to prevent a force that supports the bend of the blade between the sealing members and the developing roller from acting in a direction in which the blade is forced into contact with and away from the circumferential surface of the developing roller. As a result, an abutting force of the blade against the circumferential surface of the developing roller is invariable regardless of the presence of the sealing members. Consequently, the abutting force of the blade on the developing roller can readily be adjusted.
In the invention the other end of the blade may preferably be formed with a cutout between either end of the developing roller and the axial intermediate portion of the developing roller.
In this structure of the developing apparatus according to the invention, the bending angle of the other end of the blade at both the axial ends of the developing roller can dramatically be made different from another bending angle of the other end of the blade at the axial intermediate portion of the developing roller.